Which statement about turboprop engine fuel flow is true?

• A. SFC is low at low speed
• B. SFC is high at low speed
• C. SFC is unaffected by speed
• D. SFC is lowest at high speed

Answer: (A)

Specific fuel consumption shows how much fuel is needed to produce a given amount of thrust per hour. For turboprops, the way power is converted into forward thrust depends a lot on speed through the propeller’s efficiency. At lower airspeeds, the propeller operates in a range where a larger share of the engine’s power becomes useful thrust rather than being wasted as heat or drag. That means you get more thrust for each pound of fuel, so the fuel flow per unit thrust (the SFC) is lower. As speed increases, drag rises and the engine must burn more fuel to deliver the needed thrust, which tends to raise SFC. So the statement that SFC is low at low speed reflects how engine and propeller efficiency balance out in turboprop operation.